Blender Git Loki

Compositor: Refactor recursive methods to iterative

In order to reduce stack size this patch converts full frame
recursive methods into iterative.
- No functional changes.
- No performance changes.
- Memory peak may slightly vary depending on the tree because
now breadth-first traversal is used instead of depth-first.

Tests in D11113 have same results except for test1 memory peak:
360MBs instead of 329.50MBs.

Reviewed By: Jeroen Bakker (jbakker)

Differential Revision: https://developer.blender.org/D11515